Gravity ring

ABSTRACT

A disaster shelter for mounting under ground. The shelter includes an entranceway having at least one air vent and a substantially hollow paraboloid shaped shelter cell. The shelter cell includes a paraboloid focus portion attached to the entranceway and paraboloid base portion disposed opposite the entranceway. A gravity ring is attached to the paraboloid base portion and is dimensioned such that the shelter is constrained within the ground when the water table reaches ground level.

CLAIM OF PRIORITY

[0001] This application is a Continuation in Part of co-pending U.S.patent application Ser. No. 09/408,706, filed on Sep. 30, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of undergroundenclosures such as disaster shelters and, in particular, to means forretaining an enclosure within the ground, regardless of the level of asurrounding water table.

BACKGROUND OF THE INVENTION

[0003] History has shown that hurricanes, sudden tornadoes, anddevastating earthquakes, can cause a significant loss of property and,more importantly, of human life. There are many ways to protect oneselffrom such catastrophic events. For example, cellars that are coveredwith concrete slabs or other sturdy rigid foundations may remain intactwhen in a worst-case scenario the upper housing structure is destroyedor blown away. However, there is no guarantee that the structures abovethese cellars will not crash downward into the cellar. Further, modularor mobile homes are built upon slabs and, accordingly, offer noprotection against the devastating forces of a hurricane, tornado orearthquake.

[0004] A tornado may have swirling winds forces that can reach speeds ofover 200 MPH. This kind of wind force creates a type of suction forcethat has a tendency to pick up all sorts of structures to transport thesame to a different location. Accordingly, it is important that peoplehave strong shelters available within a short distance or in closeproximity to where they live.

[0005] A number of underground shelters have been developed to protectinhabitants in the event of a hurricane or tornado. U.S. Pat. No.5,829,208 issued Nov. 3, 1998 describes a steel reinforced cylindricalstructure having a bell-shaped end at one end and a spigot at the otherend. It is of a size to comfortably protect up to 10 people within itsinterior. One end of the structure is closed by a concrete end wallwhile the other end is partially closed by a slanting concrete deflectorwall. The deflector wall at its upper end may or may not be fastened tothe top of the cylindrical structure.

[0006] Although this structure could protect individuals from minorinclement weather, the design creates inherent problems during adisaster. First, concrete will leak while under ground for a long periodof time. Thus, during a hurricane, the structure will leak, and theporous character inherent in concrete will only be augmented by winterfreezing. Second, the cylindrical structure will not provide protectionfrom a tornado, or strong hurricane winds. While cylinders provideprotection from an evenly distributed force, a point force will crushthe structure. Third, the structure is designed to be only partiallyunderground which makes it vulnerable to heavy winds and completeexposure during a tornado, which would render the structure useless, andwould crumble in the event of an earthquake. Fourth, this structure doesnot provide a life support system to provide fresh air in the event thedisaster lasts longer than a few hours. Fifth, there are nocommunications devices in the event of a medical emergency, or inabilityto escape from the shelter because of heavy debris. Sixth, this sheltercontains no structural elements that would prevent uplifting duringtimes of high ground water. Finally, this shelter provides a singlemeans of entry and egress, creating a possibility that inhabitants willbe trapped by fallen debris.

[0007] U.S. Pat. No. 4,615,158 issued Oct. 7, 1986 describes a tornadoshelter, specially adapted for use with mobile home lots. The shelter isan underground enclosure defined by an annular sidewall and a top andbottom. The top enclosure has an entrance and egress passageway incommunication with both the enclosure and the bottom of a mobile home.

[0008] Although this shelter may provide protection from a low forcetornado which lasts for a short period of time, or a short lived weakhurricane, this shelter is not suited to protect inhabitants from aForce 5 tornado, forceful hurricane or earth quake. The invention has acylindrical shape, which only acts to disperse forces evenly over theentire structure when the force acts upon the structure evenly. If ahard force hits just one area of the structure, it will tend to buckleand destroy its integrity. The shelter is constructed from steelcylinder sidewalls and a concrete floor, which has a tendency to leakover time. This shelter provides an entranceway made of a removableboard from the floor of the mobile home, followed by a tube connectingthe mobile home to the shelter. Therefore, if the mobile home is pulledoff its foundation, the entrance tube will be openly exposed to theforceful winds of a tornado or hurricane. Since this tube is not in theground, the result will most likely be a complete destruction of theentrance tube, and therefore full exposure of the inside of the shelterto the forceful winds and rain. Finally, this shelter also lacks alllife sustaining mechanisms.

[0009] U.S. Pat. No. 4,955,166 issued Sep. 11, 1990 describes agenerally spherical tornado shelter for safely housing and protectingpeople and things underground in the form of a truncated globe that isformed from a curved sidewall and terminates in the floor at the lowerend thereof. The spherical shelter is preferably made of fiberglass andhas a generally rectangular entrance formed in spaced relation to thecentral axis and provides a doorway into the interior of the structure.A plurality of steps lead from the entrance down the floor and enablespeople to conveniently walk through the entrance, down the steps, intoand back up from the shelter.

[0010] Although this invention may provide protection from a low forcetornado, this shelter has a structural design which will render theinvention vulnerable in the event of a high force tornado or hurricane.Although made of fiberglass and virtually leak proof, the sphericalshape is inherently weak when acted upon by point forces. The entranceis rectangular in shape and therefore susceptible to destruction byheavy force winds. Finally, even if the entrance remains intact throughthe disaster, a large amount of debris may become packed against thedoorway, trapping the inhabitants inside.

[0011] In response to the above reference problems with existingshelters, the inventor of the present invention has developed a shelterthat utilizes a fiberglass shell in the form of a partial or fullparabaloid, which is buried within the-earth with one parabaloid focusfacing upward toward the level of the earth. This type of shelter isstructurally superior to the shelters noted above and, because they arenot intended to provide shelter from nuclear fallout, can be buriedfairly close to ground level. However, the combination of thewatertightness of the shelter, burial close to ground level, and thesmall amount of surface area of the shelter upon which the earth extentsits force, created the need for a means for retaining the shelter withinthe ground when the surrounding water table rises to ground level.

[0012] Prior art shelters have dealt with this problem in two distinctways. The first is to utilize concrete, either as part of the structureor as an “anchor” for the structure, to hold the structure in place. Asnoted above, concrete structures are notoriously leaky and, therefore,are not preferred. Further, the use of concrete anchors requires the useof cables or other ties from a point on the shelter to the anchor,creating point forces upon the shelter, which can reduce its structuralintegrity. Finally, the need to pour concrete at the shelter sitedramatically increases the cost of installation of the structure.Accordingly, concrete is not an acceptable means for retraining ashelter within the ground.

[0013] The second way that prior shelters have been restrained has beento bury the shelter deeply within the ground and at such an orientationso as to provide a large surface area upon which the earth may bear,effectively counterbalancing the upward buoyancy forces upon theshelter. This method has been very effective in applications, such asnuclear fallout shelters, where deep burial is desirable. However, whereweather is of primary concern, deep burial is unnecessary and addssignificantly to the cost of installation. Further, the need to increasethe structural strength of the shelter in order to accommodate theincreased ground force, and the need to provide a separate sealedentranceway in order to access the shelter, significantly increases thecost of the shelters themselves.

[0014] Therefore, there is a need for a disaster shelter that providesprotection from a tornado, hurricane, earthquake, chemical or biologicaldisaster, that will not leak while under ground for a long period oftime, that will not be crushed by a point force upon the structure, thatwill not be lifted from the ground in the event of high water table,that does not require the use of concrete anchors or concrete integralto the shelter itself, and that does not need to be buried deeply withinthe ground.

SUMMARY OF THE INVENTION

[0015] The present invention is a gravity ring and a disaster shelterupon which the gravity ring may be mounted. The combined gravity ringand disaster shelter may be shallowly buried under ground such thatshelterists are protected from natural disasters such as tornadoes andhurricanes, and from human made disasters, such as bombs, armedinvasions or the like.

[0016] In its most basic form, the gravity ring of the present inventionhas a second surface that is dimensioned for attachment to anunderground enclosure such that the downward force of the earth upon thegravity ring is transferred to the enclosure. The gravity ring alsoincludes a first surface that extends outward from the enclosure and isdimensioned such that a force exerted upon the second surface by theearth is sufficient to constrain the enclosure within the ground when awater table reaches a level of the ground. As will be discussed indetail below, although the present invention is referred to as a“gravity ring”, it is understood that the invention is not limited toconventional “rings”, but rather refers to any means forcounterbalancing a buoyancy force upon an enclosure utilizing the weightof the earth surrounding the enclosure. Accordingly, the term “gravityring” should not be read as being so limited.

[0017] In the preferred embodiment, the gravity ring is not fixedlyattached to the enclosure, but includes a second surface that is aninner surface of a substantially cylindrical ring and is dimensioned tocreate and interference fit with the top portion of a parabaloid shapedenclosure, or with an extended ridge extending from a cylindricalenclosure. The first surface of the preferred gravity ring extendsoutward and upward in the shape of a partial dome in order to increasethe surface area acted upon by the earth and to provide increasedstructural integrity over flat, flange-like, surfaces. However, in otherembodiments, the first surface may be a flat surface and the gravityring may be of a non cylindrical shape and be permanently or removablyattached to the shelter using art recognized means.

[0018] In embodiments where a full parabaloid is not utilized, thegravity ring preferably does not include an inner surface, but ratherthe first and second surfaces are portions of a continuous top surfaceof the ring. In these embodiments, the sidewalls of the enclosure areattached to the top surface of the ring along its second surface, andthe portion of the ring that extends beyond the outside of the sidewallof the enclosure forms the first surface upon which the ground bears.

[0019] In the preferred embodiment, the gravity ring is dimensioned torestrain a disaster shelter within the ground. However, it is recognizedthat the gravity ring of the present invention has broader applicationto other types of subterranean enclosures. For example, in someembodiments, the gravity ring is dimensioned to restrain an undergroundfuel storage tank, while in others it is dimensioned to restrain aseptic tank. Further, it is recognized that the gravity ring may bedimensioned to take different shapes than those dimensioned to engagethe full and partial parabaloid shaped disaster shelters disclosedherein. Accordingly, the gravity ring of the present invention shouldnot be limited to application in connection solely with the particularembodiments of the disaster shelters described herein.

[0020] In its most basic form, the disaster shelter includes anentranceway having at least one air vent and a substantially hollowshelter cell. The shelter cell includes a entrance portion attached tothe entranceway and base portion disposed opposite the entranceway. Agravity ring extends from, and exerts a downward force upon, the baseportion and is dimensioned such that the shelter is constrained withinthe ground when the water table reaches ground level.

[0021] The preferred disaster shelter includes a life support systemmade up of an air intake duct, an air filter, a blower and at least onebattery. The air filter is preferably a highly efficient particulate airfilter that filters particles from the air. The preferred blowerincludes an exhaust disposed within said shelter cell and wherein saidexhaust is positioned to create cyclonic air movement within saidshelter cell. The preferred battery comprises is a one twelve volt deepcycle battery having sufficient electrical energy, when fully charged,to power the blower to supply between 40 and 60 cubic feet per minute ofair for six days. In some embodiments a battery charger, such a solarpanel, charges the battery.

[0022] The preferred entranceway includes a substantially cylindricalmanway attached to the focus portion of the shelter cell. A hatch domering is disposed about, and extends outward from, the manway and a hatchdome cover is removably attached to the hatch dome ring such that thehatch dome cover forms a weather resistant seal with the hatch dome ringThe preferred manway includes an air inlet and an air outlet, while thepreferred hatch dome ring includes at least one inlet vent opening andat least one outlet vent opening. In such an embodiment, it is preferredthat inlet vent opening and outlet vent opening be dimensioned anddisposed relative to the air inlet and air outlet such that rain isprevented from entering the air inlet and air outlet. The preferredhatch dome cover is hatch dome ring form a substantially continuoussurface having an angle of incidence of less than twenty degrees inorder to protect the shelter from damage due to flying debris.

[0023] The preferred disaster shelter is manufactured of structuralfiberglass that is capable of withstanding up to ten pounds per squareinch of overpressure and an earthquake of an intensity of up to 8.5 on aRichter scale. An emergency escape manway is disposed through a sidewallof the preferred shelter cell to allow egress in the event that thehatch dome cover cannot be opened. Finally, the preferred shelterincludes a communications device, such as a two-way radio, forcommunicating with the outside world. In this preferred shelter, thetwo-way radio includes a retractable antenna to avoid damage during atornado or other disaster.

[0024] Therefore, it is an aspect of the invention to provide a disastershelter that provides protection from a tornado, hurricane, earthquake,chemical or biological disaster.

[0025] It is a further aspect of the invention to provide a disastershelter that will not leak while under ground for a long period of time.

[0026] It is a further aspect of the invention to provide a disastershelter that will not be crushed by a point force upon the structure.

[0027] It is a further aspect of the invention to provide a disastershelter that includes a life support system for maintaining breathableair within the shelter.

[0028] It is a further aspect of the invention to provide a gravity ringthat allows an enclosure to remain restrained in the ground in areas ofhigh water tables without the need for cables or other wires that candamage the enclosure during an earthquake or other ground shock.

[0029] It is a further aspect of the invention to provide a gravity ringthat allows an enclosure to avoid the use of concrete as part of thestructure of the enclosure.

[0030] It is a further aspect of the invention to provide a gravity ringthat allows an enclosure to be buried a short distance from the surfaceof the ground.

[0031] These aspects of the invention are not meant to be exclusive andother features, aspects, and advantages of the present invention will bereadily apparent to those of ordinary skill in the art when read inconjunction with the following description, appended claims andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a side view of one embodiment of the gravity ring of thepresent invention attached to a disaster shelter.

[0033]FIG. 2 is a side view of the preferred embodiment of the gravityring of the present invention attached to a full parabaloid disastershelter.

[0034]FIG. 3 is a top view of the preferred embodiment of the gravityring of the present invention

[0035]FIG. 4 is a cut-away side view of one embodiment of the disastershelter of the present invention.

[0036]FIG. 5 is a top isometric view of the preferred hatch dome ring.

[0037]FIG. 6 is a cut away isometric view of the preferred embodiment ofthe disaster shelter of the present invention.

[0038]FIG. 7A is an end view of an underground storage tank utilizing analternative embodiment of the gravity ring.

[0039]FIG. 7B is an end view of the embodiment of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Referring first to FIG. 1, a side view of one embodiment of thedisaster shelter 10 is shown. The disaster shelter 10 includes asubstantially hollow paraboloid shaped shelter cell 12 and anentranceway 14 having at least one air vent opening 22 disposedtherethrough. The shelter cell 12 is preferably manufactured ofstructural fiberglass and is oriented such that the paraboloid focusportion 16 is attached to entranceway 14 and the paraboloid base portion18 is disposed opposite of the entranceway 14. The preferred sheltershell is a paraboloid bell having a 1:1.7 elliptical ratio. Thisparaboloid shape optimizes the structural integrity of the fiberglass,as it will not buckle or be destroyed by strong point forces.

[0041] In the embodiment of FIG. 1, the gravity ring 20 is attached to,and surrounds the paraboloid base portion 18. The gravity ring 20 allowsthe system to remain constrained within the ground, even in areas wherethe water table reaches ground level, without the need for separatetie-downs or bulky concrete footings, where the water table, below whichthe ground is completely saturated with water. Under this circumstance,the disaster shelter 10 displaces water creating approximately 28,900lbs. of hydrostatic pressure or upward “buoyancy” force, but is heldstable in the ground by the gravity ring 20, which generatesapproximately 35,650 pounds of downward “gravity” force. Such a positivegravity force allows the disaster shelter 10 of the present invention tobe restrained underground without the need for separate restrainingcables, as are commonly used to restrain underground tanks. Theelimination of these cables is a significant benefit as they create verylocalized stress, which may damage the structure during ground shockfrom heavy traffic or earthquakes. Conversely, the gravity ring 20creates uniform stresses around the disaster shelter 10, effectivelyeliminating local stresses.

[0042] Although the gravity ring 20 of FIG. 1 is shown as being attachedto the base portion 18 of a partial parabaloid shelter cell 12, thereare a number of different ways in which the gravity ring 20 may beutilized. As shown in FIGS. 2 and 3, a separate and removable gravityring 120 forms an interference fit with a full parabaloid shelter cell122. The gravity ring 120 of FIGS. 2 and 3 includes a second surface 130that forms a cylinder having a diameter D, which is dimensioned toengage the outer surface of the shelter cell 122. As shown in FIG. 2,the preferred diameter D is equal to approximately ninety nine percent(99%) of the maximum diameter of the parabaloid shelter cell 122.However, the second surface 130 may take any dimension, so long as itwill allow the gravity ring to engage the enclosure.

[0043] In some embodiments, such as those in which a cylindrical tank(not shown) is buried on its end, the tank may include a flange orseries of shelves disposed about the outside surface and the diameter Dmay be dimensioned to be slightly larger than the diameter of the tank.In these embodiments, the first surface is not the inside cylindricalsurface, but is part of the bottom surface of the ring 120 that engagesthe flange. Similarly, gravity rings may be dimensioned to engageflanges or shelves disposed upon the outsides of other non-cylindricaltanks in substantially the same manner. Accordingly, the gravity ring120 should not be seen as being limited to interference fit rings orrings that are substantially cylindrical.

[0044] The gravity ring of FIGS. 2 and 3 also includes a first surface128 that extends outward from the shelter cell 122 and is dimensionedsuch that a force exerted upon the second surface 128 by the earth issufficient to constrain the shelter cell 122 within the ground when awater table reaches a level of the ground. In the preferred embodiment,the surface area of the first surface 128 is designed to exert onehundred and twenty percent (120%) of the upward buoyancy force exertedupon the shelter, given a ground density of seventy pounds per cubicfoot. This calculation provides an adequate factor of safety, and meetsthe requirements of current underground enclosure standards. However, itis recognized that a calculation using a smaller percentage relative tobuoyancy, or a higher ground density, may be utilized, provided thetotal is at least equal to the total buoyancy force exerted when thewater table reaches ground level.

[0045] The gravity ring of FIGS. 2 and 3 is preferably manufactured ofstructural fiberglass and is dimensioned such that the first surface 128extends upward in the form of a dish. In the preferred embodiment, theradius R formed by the first surface 128 is equal to one half of thediameter D of the second surface 130 of the gravity ring. This ispreferred as it provides a structurally stable member having increasedsurface area upon which the ground may bear. However, it is recognizedthat gravity rings 120 having different cross sections may besubstituted to achieve similar results.

[0046] As noted above, it is preferred that the gravity ring anddisaster shelter be manufactured of structural fiberglass. Althoughother materials, such as stainless steel and the like, may be utilized,structural fiberglass is preferred for a number of reasons. First,fiberglass provides extremely high resiliency and corrosion resistanceand has a tendency to remain intact if overstressed. Second, it may beeasily shaped into the hollow compound curved structure that makes upthe paraboloid shelter cell 12. Third, fiberglass forms a complete vaporbarrier, which provides a dry atmosphere when placed below ground, andit has proven to be sound in the underground storage tank industry.Fourth, structural fiberglass is a poor thermal conductor so there islittle to no “sweating” on the inside walls during occupancy. Finally,structural fiberglass does not conduct electricity. This is important ashurricanes and tornadoes commonly have severe and numerous lightingstrikes often topple power poles and above ground structures leavinglive electrical wires sparking on the ground. Accordingly, a disastershelter 10 manufactured from structural fiberglass is safe to use evenif in direct contact with live power lines or directly struck bylightning.

[0047] Referring now to FIG. 4, the inside of one embodiment of thedisaster shelter 10 is shown. This embodiment includes a life supportsystem 24 that provides breathable air to the occupants of the shelter10. The life support system 24 includes an air intake duct 26 in fluidcommunication with an air vent (not shown). An air filter 28 is in fluidcommunication with the air intake duct 26 and acts to filter theincoming air. A blower 30 is in fluid communication with the outlet ofthe air filter 28 and circulates the air within the shelter cell 12.Finally, at least one battery 32 is placed in electrical communicationwith the blower 30, providing power to allow the blower to operate.

[0048] As shown in FIG. 4, the air intake duct 26 enters the sheltercell 12 through an opening in the shelter cell 12. However, in otherembodiments, such at the embodiment of FIG. 5, the air intake duct 26 isdisposed entirely within the shelter cell 12 and is in communicationwith the air vent via an air inlet 27 disposed through the entranceway14. The air intake duct 26 is preferably manufactured of corrugatedplastic smooth bore hose. However, other art recognized duct materialsmay be substituted to achieve similar results.

[0049] The air filter 28 receives the incoming air from the air intakeduct 26 and filters it in a predetermined manner. In the preferredembodiment, the air filter 28 is a highly effective particulate airfilter (hereafter HEPA filter) that is capable of removing 99.99% ofparticles, larger than 0.3 microns in size, from the air. Accordingly,the HEPA filter will remove all physical particles such as dust,aerosols, and pollen, from the incoming air. In other embodiments,however, the air filter 28 also includes a carbon filter (not shown) forfiltering chemical and biological contaminants from the air. Such acarbon filter would preferably include both an activated carbon filtermedium and a whetlerite carbon filter medium and would be disposed atthe outlet of the HEPA filter.

[0050] The blower 30 is in fluid communication with the outlet of theair filter 28. The The preferred blower is a battery-powered reversecurve motorized impeller. This preferred blower has a 60,000 hour lifeand supplies an air stream of 40 cubic feet per minute (CFM) into theinterior of shelter cell 12. Given an interior volume of 474 cubic feetin the preferred shelter cell 12, the preferred blower 30 provides anair change within the shelter cell 12 every twelve minutes. The exhaustof the blower 30 is preferably positioned such that it creates cyclonicair movement within the shelter. The warm spiraling spent air rises upto vent out around the hatch dome. This air may be exhausted through thesame air vent 27 through which incoming air is taken. However, as shownin FIGS. 4 and 5, exhaust air may also be vented through a dedicated airoutlet 29. The air supply rate and positioning of the preferred blower30 places the shelter under positive pressure and has proven to workextremely well at maintaining constant oxygen, carbon dioxide, andmoisture levels.

[0051] The preferred blower 30 includes an on/off switch that allows theblower 30 to be disengaged when ground fires, or other airbornecontaminants, are present around the hatch dome. During such a time, theshelterists must breathe in a sealed shelter atmosphere. The safeduration time for sealed operation is based on a 3% carbon dioxide limitand, therefore, is a function of the number of shelterists, degree ofphysical activity of the shelterists, and the volume of the shelter cell12 above the floor 34. In the preferred embodiment, six shelterists whoare mildly active can be in the shelter cell 12 for approximately 4hours before reaching the 3% CO₂ limit.

[0052] The battery 32 provides power to the blower 30, as well as toother electrically powered devices, such as lights, two-way radio's,scanners or the like, that are utilized within the shelter cell 12. Inthe preferred embodiment, the battery 32 is made up of three, twelvevolt-110 amp deep cycle marine batteries contains sufficient electricalenergy, when fully charged, to power the blower for up to six days atair flow rates of 40 and 60 cubic feet per minute. However, otherbatteries, having different power levels and providing different usefullives, may be utilized to achieve similar results. During non-disastertime, the battery 32 will suffer a very minor loss of charge.Accordingly, the preferred disaster shelter 10 also includes a batterycharger 36 for recharging the battery. In some embodiments, a solarpanel (not shown) made up of photovoltaic cells is disposed above thelevel of the ground 42 and are wired to the battery 32. In this manner,the battery 32 is allowed to trickle charge via the electrical energygenerated by the solar panel 38. However, in other embodiments,different battery chargers 36 may be utilized. For example, the battery32 may be charged by an automobile and a heavy-duty set of jumper cablesrun from the automobile through the entranceway 14 to the battery 32.

[0053] The embodiment of FIG. 4 also includes an emergency escape manway44 disposed through the side wall 46 of the shelter cell 12 to provide ameans of egress from the shelter in the event that the entranceway 14 isunable to be opened due to heavy debris or damage. If a heavy object,such as a car, comes to rest on top of the entranceway 14, the emergencyescape manway 44 provides the shelterist with the ability to dig upwardsand sideways to get around the object. Accordingly, it is preferred thatcrushed stone be used to backfill around the emergency escape manway 44if the disaster shelter 10 is installed in cold climates where theground freezes.

[0054] The preferred embodiment of the emergency escape manway 44includes a manway cover 48 that may be unbolted from the inside of theshelter cell 12 to allow shelterists to dig upwards to the level of theground 42. After an emergency exit, the preferred manway cover 48 may bere-bolted and backfill material can be taken up to the surface using afive-gallon bucket and rope and re-backfilled.

[0055] In the embodiment of FIG. 4, the entranceway 14 is made up of asubstantially cylindrical manway 50 attached to said focus portion 16 ofsaid shelter cell 12. A hatch dome ring 52 is disposed about, andextends outward from, the manway 50. Finally, a hatch dome cover 54 isremovably attached to the hatch dome ring 52 such a weather resistantseal is formed between the hatch dome cover 54 and the hatch dome ring52. The hatch dome cover 54 is preferably of a dome shape and isdimensioned to sit within a groove 56 in the hatch dome ring 52. In someembodiments, a common gasket is applied between the groove 56 and hatchdome cover 54 to enhance leak protection. When mounted to the preferredhatch dome ring 52, the preferred hatch dome cover 54 and hatch domering 52 form a dome having an angle of incidence A of approximatelytwenty degrees (20°). This low angle of incidence A prevents the shelter10 from being displaced by high winds and allows the hatch dome cover 54and hatch dome ring 52 to deflect flying debris during a tornado orhurricane without damage.

[0056] The preferred hatch dome cover 54 and hatch dome ring 52 are madeof an intumescent laminate material called COMBAT COMPOSITE™ material,which is a structural fire-and bullet-resistant laminate developed byRadius Defense Inc. of Northwood, N.H. The hatch dome is also designedto protect the shelter from a fire reaching 1700° F. for one hour whilemaintaining its structural integrity in compliance to A.S.T.M. E119.This design and material makes the preferred shelter 10 very stealthy.It produces little or no thermal signature, little or no metallicsignature, and little or no radar signature, making it almost impossibleto be detected by modern target acquisition equipment. Although thehatch dome cover 54 is not impenetrable, it is manufactured according toThe National Institute of Justice (NIJ) standards from Class 0 up toClass IV to resist penetration by various threats, and is specificallydesigned to resist seven basic assaults from people trying to break intothe shelter.

[0057] As shown in FIG. 4, the hatch dome cover 54 may be secured fromthe inside of the shelter cell 12 via a locking mechanism 58, such as apivot hinge 59. The preferred pivot hinge 59 is a stainless steelvertical pivot hinge that mounted inside of the entranceway 14 and iscapable of lifting the hatch dome cover 54 even when it is covered withup to six tons of debris. In another embodiment, the locking mechanism58 utilizes an external hinge that fits within a pocket (not shown) inthe hatch dome ring 52 and an integral locking bar, which secures thehatch dome cover 54 to the hatch dome ring 52. The combination of theintegral hinge and locking bar allows the hatch dome cover 54 to bequickly closed and locked in the event that a shelterist is pursued byan intruder, and to resist pressures of negative 5 PSIG created by ablast or tornado. In the preferred embodiment, the hatch dome cover 54is connected to the hatch dome ring by an external recessed hinge whichallows the hatch dome cover 54 to open 160 degrees. This allows fast andeasy submarine type entry. Three self-positioning forged hatch clampssecure the hatch dome cover 54. In this preferred embodiment, each hatchclamp is designed to resist 5000 lbs. of uplifting force caused by thenegative pressure of a tornado or explosion. Once the hatch dome cover54 is pulled closed, the three spring-loaded hatch clamps are rotated byhand 90 degrees and the wing nut on each hatch clamp is tightened byhand.

[0058] Referring now to FIG. 5, an isometric view of the preferred hatchdome ring 52 is shown. As noted above, the hatch dome ring 52 isdisposed about, and extends outward from, the manway 50. In this manner,the hatch dome ring 52 and acts to shield the air inlet 27 and airoutlet 29 from the elements. The preferred hatch dome ring 52 is mountedwith its bottom rim 60 disposed at ground level to prevent high windsfrom hitting the underside of the hatch dome ring 52. Thus, the topsurface 62 of the hatch dome ring 20 includes at least one inlet ventopening 64 and at least one outlet vent opening 66 to allow gasses toenter and exit the area between the hatch dome ring and the manway 50.The top surface 62 of the preferred hatch dome ring 52 also includes arecessed groove 56 disposed about the open top for mating with the hatchdome cover (not shown) and at least one notch 74 that is sized to allowa hinge to be utilized to attach the hatch dome cover to the hatch domering 20. In addition, a number of rain gullies 76 may be utilized todrain trapped water from the area surrounding the recessed groove 56.

[0059] In the preferred embodiment, multiple small vent openings 64, 66are utilized to provide sufficient airflow to and from the air inlet 27and air outlet 29. These vent openings 64, 66 are preferably sized toprevent sabotage by an intruder utilizing an implement, such as agrappling hook. The vent openings 64, 66 on the top surface 62 of thehatch dome ring 52 are preferably not disposed directly above the airinlet 27 and air outlet 27. This arrangement causes a venturi effect,where the air and rain pass through the openings 64, 66 at high velocityand immediately slow upon entering the area under the hatch dome ring52, effectively dropping to the rain to the ground prior to enteringeither the air inlet 27 or air outlet 29. The bottom surface 68 of thepreferred hatch dome ring 20 includes a pair of baffles 70, 72. Thesebaffles 70, 72 are disposed in predetermined locations relative to theair inlet 27 and air outlet 29 in order to prevent gasses exhaustedthrough the air outlet 29 from being sucked into the air inlet 27.

[0060] In some embodiments of the invention, an entranceway such as thatdisclosed in the Applicant's co-pending application Ser. No. 09/330,870,titled ENTRANCEWAY AND DISASTER SHELTER UTILIZING THE SAME, andincorporated herein by reference, is utilized. In still otherembodiments, a variation of the entranceway of the Applicant'sco-pending application is utilized. This alternative entranceway 14,shown with reference to FIGS. 5-7, includes a leaching septic tank 102 avertically oriented HEPA filter 104, and a plunger valve 118 disposedbetween the air inlet 27 and HEPA filter 104.

[0061] As shown in FIG. 6, the preferred septic tank 102 is an extrudedhalf-paraboloid tank that is designed to withstand external pressure ofat least 50 PSIG, such as is generated by a nuclear blast or heavytraffic over the shelter. The septic tank 102 includes a plurality ofopenings 106 that allow solid waste to collect within the tank 102,while allowing liquid waste to leach out into the surrounding soil. Theseptic tank 102 includes a pump port 108 that allows the solid andliquid wastes to be manually pumped from the tank 102. The pump port 108is preferably disposed upon the top of the tank 102 and, when installed,is located approximately twelve inches below the level of the ground andmust be excavated prior to pumping. However, in other embodiments, anextension pipe (not shown) between the pump port 108 and ground levelmay be included to eliminate this need to excavate. The preferred septictank 102 also includes a septic vent 110 that passes from the tank 102and terminates under the hatch dome ring 52 and allows gasses, such asmethane, generated during decomposition to vent through the outlet ventopening 66 to the surrounding atmosphere. The vertically oriented HEPAfilter 104 conserves space around the entranceway 14 and allows a cleartwenty-four inch diameter manway opening to be utilized.

[0062] Referring again to FIG. 6, the shelter 10 is dimensioned to allowa shelterist 80 to comfortably stand within the shelter cell 12. Inaddition to the features discussed above, the preferred disaster shelter10 also includes a communication device 82 and a light 84 in electricalcommunication with the battery 32. It is preferred that that light 84 beflourescent light, due to the low power requirements and low heatgeneration of such lights. However, incandescent lights 84 may beutilized to achieve similar results. The preferred communication device82 includes a pair of radios, such as a 12-volt CB/weather band radioand scanner.. The CB/weather radio allows shelterists to keep track oftornado activity and allows two-way communications to local people. Theoptional scanner allows monitoring of all AM, FM, search and rescue,fire, police, aircraft, weather, and numerous other frequencies in thelocal area.

[0063] Referring now to FIGS. 7A and 7B, an alternative embodiment ofthe gravity rings is shown. In this embodiment, adapted for use with acylindrical underground storage tank 222 mounted horizontally within theground, the gravity ring is made up of two semi-cylindrical extensions220 that are attached to, and project outward from, either end 224 ofthe tank 222. As was the case with the gravity rings discussed above,these extensions 220 each include a first surface 230 that isdimensioned to transfer a downward force generated by the ground to thetank in order to counterbalance the upward buoyancy force created whenthe water table reaches ground level.

[0064] The gravity ring of FIGS. 7A and 7B is preferably mounted to thebottom of a storage tank via art-recognized means. In cases where thetanks are manufactured to metal, this may be via welding or bolting. Incases where fiberglass tanks are utilized, the extensions 220 may belaminated directly to the bottom of the tank or formed integral thereto.

[0065] Although the present invention has been described in considerabledetail with reference to certain preferred versions thereof, otherversions would be readily apparent to those of ordinary skill in theart. Therefore, the spirit and scope of the appended claims should notbe limited to the description of the preferred versions containedherein.

What is claimed is:
 1. A gravity ring for restraining an enclosure belowa quantity of earth, wherein said quantity of earth forms a groundlevel, and wherein said gravity ring comprises: a first surface thatextends outward from an outer surface of said enclosure, said secondsurface being dimensioned such that a force exerted upon the secondsurface by said quantity of earth disposed upon said first surface issufficient to constrain said enclosure below said ground level when awater table reaches said ground level; and a second surface incommunication with said first surface, wherein said second surface isdimensioned for engagement with said enclosure such that said downwardforce exerted upon said first surface by said quantity of earth istransferred through said second surface to said enclosure.
 2. Thegravity ring as claimed in claim 1 wherein said second surface is aninner surface of a substantially cylindrical ring.
 3. The gravity ringas claimed in claim 2 wherein said enclosure comprises a parabaloidshaped top portion and wherein second surface is dimensioned to createan interference fit with said outer surface of said enclosure.
 4. Thegravity ring as claimed in claim 2 wherein said first surface isdimensioned to form a curved inner surface extending upward towards saidground level.
 5. The gravity ring as claimed in claim 4 wherein saidenclosure comprises a parabaloid shaped top portion and wherein secondsurface is dimensioned to create an interference fit with said outersurface of said enclosure.
 6. The gravity ring as claimed in claim 1wherein said gravity ring is manufactured of a fiberglass compositematerial.
 7. The gravity ring as claimed in claim 6 wherein saidenclosure is manufactured of a fiberglass composite material and whereinsaid gravity ring is attached to said enclosure.
 8. The gravity ring asclaimed in claim 7 wherein said gravity ring is substantiallypermanently attached to said enclosure.
 9. The gravity ring as claimedin claim 7 wherein said enclosure is removably attached to saidenclosure.
 10. A disaster shelter for mounting below a quantity ofearth, wherein said quantity of earth forms a ground level, and whereinsaid disaster shelter comprises: an entranceway; a shelter cell, saidshelter cell having an entrance portion attached to said entranceway andbase portion disposed opposite said entranceway; and a gravity ringdisposed about said base portion, said gravity ring comprising; a firstsurface that extends outward from an outer surface of said shelter cell,said second surface being dimensioned such that a force exerted upon thesecond surface by said quantity of earth disposed upon said firstsurface is sufficient to constrain said shelter below said ground levelwhen a water table reaches said ground level; and a second surface incommunication with said first surface, wherein said second surface isdimensioned for engagement with said shelter cell such that saiddownward force exerted upon said first surface by said quantity of earthis transferred through said second surface to said shelter cell.
 11. Thedisaster shelter as claimed in claim 10 wherein said entrance portion ofsaid shelter cell is dimensioned to form a partial parabaloid having aparaboloid focus portion attached to said entranceway.
 12. The disastershelter as claimed in claim 11 wherein said entrance portion and saidbas portion of said shelter cell to form a substantially full parabaloidshaped shelter cell.
 13. The disaster shelter as claimed in claim 11wherein said entranceway further comprises a substantially cylindricalmanway attached to said focus portion of said shelter cell, a hatch domering disposed about, and extending outward from, said manway, and ahatch dome cover removably attached to said hatch dome ring such thatsaid hatch dome cover forms a weather resistant seal with said hatchdome ring
 14. The disaster shelter as claimed in claim 10, wherein saidshelter cell is manufactured of structural fiberglass.
 15. The disastershelter as claimed in claim 10 further comprising an emergency escapemanway disposed through a sidewall of said shelter cell.
 16. Anunderground enclosure for mounting below a quantity of earth, whereinsaid quantity of earth forms a ground level, and wherein said enclosurecomprises: a substantially hollow tank portion; and a gravity ringdisposed about said tank portion such that said gravity ring applies adownward force upon said tank portion, said gravity ring comprising; afirst surface that extends outward from an outer surface of said tankportion, said second surface being dimensioned such that a force exertedupon the second surface by said quantity of earth disposed upon saidfirst surface is sufficient to constrain said tank portion below saidground level when a water table reaches said ground level; and a secondsurface in communication with said first surface, wherein said secondsurface is dimensioned for engagement with said tank portion such thatsaid downward force exerted upon said first surface by said quantity ofearth is transferred through said second surface to said tank portion.17. The underground enclosure as claimed in claim 16, wherein said tankportion comprises a substantially cylindrical tank portion and whereinsaid gravity ring comprises a first extension portion extendingoutwardly from a first end of said tank portion and a second extensionportion extending outwardly from a second end of said tank portion. 18.The underground enclosure as claimed in claim 17 wherein at least aportion of said tank portion and said gravity ring are manufactured ofstructural fiberglass.